U.S. patent number 5,156,820 [Application Number 07/351,829] was granted by the patent office on 1992-10-20 for reaction chamber with controlled radiant energy heating and distributed reactant flow.
This patent grant is currently assigned to Rapro Technology, Inc.. Invention is credited to Yen-Hui Ku, Fred Wong.
United States Patent |
5,156,820 |
Wong , et al. |
October 20, 1992 |
**Please see images for:
( Certificate of Correction ) ** |
Reaction chamber with controlled radiant energy heating and
distributed reactant flow
Abstract
A reaction chamber for a controlled reaction on a reaction
surface of a sample provides for controlled distribution of radiant
energy over the reaction surface to offset radiant heat loss of the
sample, and establishes uniform distribution of reactant flow on
the sample. A lamp housing supplies radiant energy over the sample,
which absorbs at least a component of the radiant energy. A support
member which supports the sample within the reaction chamber is
formed of a material which is essentially transparent to the
radiant energy so that it does not behave as a susceptor. An array
of lamps, is mounted with the reaction chamber so that direct
radiant energy is transmitted through a window to the reaction
surface of the sample. A reflecting surface on the housing includes
a lamp seat for each lamp in the array with an individually
specified position, curvature and tilt with respect to the reaction
surface. A source of reactant gas is coupled through a gas port to
the reaction chamber between the window and the reaction surface. A
reactant distribution plate is mounted between the gas port and the
reaction surface, and causes distributed flow of reactant gas over
the reaction surface. The distribution plate includes a plurality
of perforations having a pattern which determines the distribution
of reactant gas flow.
Inventors: |
Wong; Fred (Fremont, CA),
Ku; Yen-Hui (Sunnyvale, CA) |
Assignee: |
Rapro Technology, Inc.
(Fremont, CA)
|
Family
ID: |
23382589 |
Appl.
No.: |
07/351,829 |
Filed: |
May 15, 1989 |
Current U.S.
Class: |
422/186.05;
438/935; 392/416; 392/418; 118/725; 118/730; 427/248.1 |
Current CPC
Class: |
B01J
19/0013 (20130101); B01J 19/122 (20130101); C30B
25/105 (20130101); C30B 31/12 (20130101); C23C
16/481 (20130101); B01J 2219/00058 (20130101); Y10S
438/935 (20130101) |
Current International
Class: |
B01J
19/00 (20060101); B01J 19/12 (20060101); C30B
31/00 (20060101); C30B 25/10 (20060101); C30B
31/12 (20060101); C23C 16/48 (20060101); B01J
019/08 (); B01J 019/12 () |
Field of
Search: |
;118/724,725,728,729,730
;437/233,243,925,967,963 ;427/248.1 ;219/339 ;422/186.05 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Van Pul et al., Manufacturing Methods, Techniques and Automated
Controls for the Continuous Epitaxial Processing of Silicon
Integrated Circuits, vol. 1, Technical Report AFML-TR-78-47, May,
1978, Motorola, Inc..
|
Primary Examiner: Eldred; J. Woodrow
Attorney, Agent or Firm: Fliesler, Dubb, Meyer &
Lovejoy
Claims
What is claimed is:
1. An apparatus for supplying radiant energy over a sample having a
reaction surface, the sample absorbing at least a component of the
radiant energy, and characterized by a nonuniform distribution of
heat loss, the apparatus comprising:
a reduced-pressure reaction chamber having a wall;
means, coupled with the reaction chamber, or cooling the wall of
the reaction chamber;
means, mounted with the reaction chamber, for supporting the sample
within the reaction chamber, and including a thermally inert
support member contacting the sample,;
means, mounted with the reaction chamber, for generating radiant
energy; and
energy distribution means, mounted with the means for generating,
for distribution the radiant energy generated by the means for
generating to form a controlled distribution of radiant energy at
the reaction surface, and wherein the controlled destruction of
radiant energy offsets the nonuniform distribution of heat loss on
the sample.
2. The apparatus of claim 1, wherein the support member is mounted
within a shadow of the sample so that the radiant energy does not
directly strike the support member.
3. The apparatus of claim 1, wherein the support member within the
reaction chamber includes three sample contact points defining a
support plane and contacting the sample.
4. The apparatus of claim 1, wherein the support member consists of
material essentially transparent to the radiant energy.
5. An apparatus for supplying radiant energy over a sample having a
reaction surface, the sample absorbing at least a component of the
radiant energy, and characterized by a nonuniform distribution of
that loss, the apparatus comprising:
a reaction chamber;
means, mounted with the reaction chamber, for supporting the sample
within the reaction chamber;
means, mounted with the reaction chamber, or supporting the sample
within the reaction chamber;
means, mounted with the reaction chamber, or generating radiant
energy; and
energy distribution means, mounted with the means for generating,
for distributing the radiant energy generated by the means or
generating to from a controlled distribution of radiant energy at
the reaction surface, and wherein the controlled distribution of
radiant energy offsets the nonuniform distribution of heat loss of
the sample;
wherein the means for generating radiant energy includes a
plurality of lamps; and the energy distribution means
comprises:
a lamp housing having a lamp seat for each of the plurality of
lamps, each lamp seat having a reflective surface and the
reflective surface of at least one lamp seat has a first portion
with a first tilt with respect to a plane parallel to the reaction
surface, and a second portion with a second tilt with respect to
the plane parallel to the reaction surface.
6. The apparatus of claim 5, wherein the means for supporting
includes:
a support member within the reaction chamber supporting the sample
so that the reaction surface faces the energy distribution means;
and
means, coupled to the support member, for rotating the support
member about an axis perpendicular to the reaction surface.
7. The apparatus f claim 6, wherein the plurality of lamps includes
liner lamps.
8. The apparatus of claim 5, wherein the reflective surfaces of the
lamp seats have conical curvatures.
9. The apparatus of claim 7, wherein he reflective surfaces of the
lamp seats have conical curvatures.
10. The apparatus of claim 1, further including:
means, coupled to the reaction chamber, for sensing a temperature
of the reaction surface.
11. The apparatus of claim 1, further including:
means, coupled of the means for generating, for controlling
intensity of the radiant energy.
12. The apparatus of claim 5, further including:
means, coupled to the plurality of lamps, or individually
controlling intensity of each of the plurality of lamps.
13. An apparatus for supplying radiant energy over a sample having
a reaction surface, the sample absorbing at least a component of
the radiant energy, and characterized by a nonuniform distribution
of hat loss, the apparatus comprising:
a reacting chamber;
means, mounted with the reaction chamber, for supporting the sample
within the reaction chamber;
means, mounted with the reaction chamber, for generating radiant
energy; and
energy distribution means, mounted with the means for generating,
for distributing the radiant energy generated by the means for
generating to form a controlled distribution of radiant energy at
the reaction surface, and wherein the controlled distribution of
radiant energy offsets the nonuniform distribution of heat loss of
the sample;
wherein the reaction chamber includes a window on the reaction
chamber through which the radiant energy enters the reaction
chamber and wherein the window consists of a material that is
essentially transparent to radiant energy in a first range absorbed
by the sample, and that absorbs a long infrared range of radiation
generated by the means for generating radiant energy, and has a
thickness sufficient to filter the long infrared range of radiation
so that the long infrared range does no the at inside the reaction
chamber.
14. An apparatus for supplying a flow of a gas reactant over a
reaction surface on a sample, the sample absorbing radiant energy
within a given range of wavelengths, comprising:
a reaction chamber having a window essentially transparent to
radiant energy in the given range;
means, mounted with the fraction chamber, for supporting the sample
within the reaction chamber, so that the reaction surface on the
sample faces the window;
means, in gas flow communication with the reaction chamber, for
supplying a flow of reactant gas to the chamber between the window
and the reaction surface;
pump means, having an exhaust port in gas flow communication with
the reaction chamber, for pumping gas out of the reaction chamber
to maintain a reduced pressure within the reaction chamber; and
a reactant distribution means, mounted int eh reaction chamber
between the reaction surface and the means for supplying reactant
gas, and essentially transparent to radiant energy in the given
range, for directing a distributed flow of reactant gas essentially
perpendicular to the reaction surface.
15. The apparatus of claim 14, wherein the reactant distribution
means, reaction surface and exhaust port define an essentially
radially symmetric gas flow path over the reaction surface through
the reaction chamber.
16. The apparatus of claim 15, wherein the reaction surface is
between the reactant distribution means and the exhaust port.
17. The apparatus of claim 14, wherein the reactant distribution
means includes:
a plate, mounted between the window and the reaction surface
forming receiving compartment of the reactant gas, the plate
essentially transparent to the given range of radiant energy and
having a plurality of perforations providing distributed gas flow
communication between the receiving compartment and the reaction
surface.
18. The apparatus of claim 17, wherein the means for supplying a
flow of reactant gas includes:
a plurality of gas ports connected to supply reactant gas, in gas
flow communication with the receiving compartment.
19. An apparatus for supplying a flow of a gas reactant over a
reaction surface on a sample, the sample absorbing radiant energy
within a given range of wavelengths, comprising:
a reaction chamber having a window essentially transparent to
radiant energy in the given range;
means, mounted with the reaction chamber, for supporting the sample
within the reaction chamber, so that the reaction surface on the
sample faces the window;
means, in gas flow communication with the reacting chamber, for
supplying a flow of reactant gas to the chamber between the window
and the reaction surface; and
a reactant distribution means, mounted in the reaction chamber
between the reaction surface and the means for supplying reactant
gas, and essentially transparent to radiant energy in the given
range, for directing a distributed flow of reactant gas essentially
perpendicular to the reaction surface; wherein the means for
supporting includes:
a support member within the reaction chamber supporting the sample
so that the reaction surface faces the reactant distribution means;
and
means, coupled to the support member, for rotating the support
member about an axis perpendicular to the reaction surface.
20. The apparatus of claim 17, wherein the means for supporting
includes:
a support member within the reaction chamber supporting the sample
so that the reaction surface faces the reactant distribution means;
and
means, coupled to the support member, of rotating the support
member about an axis perpendicular to the reaction surface.
21. The apparatus of claim 14, wherein the means for supporting
includes a support member within the reaction chamber contact the
sample, and the support member is mounted within a shadow of the
sample so that the support member does not deflect the flow of
reactant gas onto the reaction surface.
22. The apparatus of claim 14, wherein the means for supporting
includes a support member within the reaction chamber with three
sample contact points defining a support plane and contacting the
ample.
23. An apparatus for supplying a flow of a gas reactant over a
reaction surface on a sample, the sample absorbing radiation energy
within a given range of wavelengths, comprising:
a reaction chamber having a wall and a window essentially
transparent to radiant energy in the given range;
means of cooling the wall of the reaction chamber;
means, mounted with the reaction chamber, for supporting the sample
within the reaction chamber, so that the reaction surface on the
sample faces the window, and including a thermally inert support
member contacting the sample;
means, in gas flow communication with the reaction chamber, for
supplying a flow of reactant gas to the chamber between the window
and the reaction surface; and
a reactant distribution means, mounted in the fraction chamber
between the reaction surface and the mans for supplying reactant
gas, and essentially transparent to radiant energy in the given
range, for directing a distributed flow of reactant gas essentially
perpendicular to the reaction surface.
24. The apparatus of claim 23, wherein the window consists of a
material that absorbs a long infrared range of radiation, and has a
thickness sufficient to filter the long infrared range of radiation
so that the long infrared range does not heat inside the reaction
chamber.
25. An apparatus for inducing a controlled reaction on a reaction
surface on a sample, the sample absorbing radiant energy within a
given range of wavelengths, and characterized by a nonuniform
distribution of heat loss, the apparatus comprising:
a reaction chamber having a wall and a window essentially
transparent to radiant energy in the given range;
means, coupled with the reaction chamber, for cooling the wall of
the reaction chamber;
support means, mounted with the reaction chamber, for supporting
the sample within the reaction chamber, so that the reaction
surface faces the window, and including a thermally inert support
member contacting the sample;
means, mounted with the fraction chamber outside the window, for
generating radiant energy in the given range;
energy distribution means, mounted with the means for generating,
for distributing the radiant energy in the given range to form a
controlled distribution of radiant energy at the reaction surface
of the sample, and wherein the controlled distribution of radiant
energy offsets the nonuniform distribution of heat loss on the
sample;
means, in gas flow communication with the reaction chamber, for
supplying a flow of reactant gas to the chamber between the window
and the sample; and
a reactant distribution means, mounted in the reaction chamber
between the reaction surface on the sample and the means for
supplying reactant gas, and transparent to radiant energy in the
given range, for distributing the flow of reactant gas to create a
distributed flow over the reaction surface on the sample.
26. The apparatus of claim 25, further including:
exhaust means, having an exhaust port in gas flow communication
with the reaction chamber, for pumping gas out of the reaction
chamber to maintain a reduced pressure within the reaction
chamber.
27. The apparatus of claim 25, wherein the window consists of a
material that absorbs a long infrared range of radiation generated
by the means for generating radiant energy, and has a thickness
sufficient to filter the long infrared range of radiation so that
the long infrared range does not heat inside the reaction
chamber.
28. The apparatus of claim 26, wherein the reactant distribution
means, reaction surface and exhaust port define a gas flow path
essentially perpendicular to the reaction surface and essentially
radially symmetric through the reaction chamber.
29. The apparatus of claim 28, wherein the reaction surface is
between the reactant distribution means and the exhaust port.
30. The apparatus of claim 25, wherein the reactant distribution
means includes:
a plate, mounted between the window and the reaction surface
forming receiving compartment for the reactant gas, the plate
essentially transparent to the given range of radiant energy and
having a plurality of perforations providing distributed gas flow
communication between the receiving compartment and the reaction
chamber.
31. The apparatus of claim 30, wherein the means for supplying a
flow of reactant gas includes:
a plurality of gas ports connected to supply reactant gas, in gas
flow communication with the receiving compartment.
32. The apparatus of claim 25, wherein the
support member supports the sample so that the reaction surface
faces the reactant distribution means; and the support means
further includes:
means, coupled to the support member, for rotating the support
member bout an axis a perpendicular to the reaction surface.
33. The apparatus of claim 30, wherein the
support member supports the sample so that the reaction surface
faces the reactant distribution means; and the support means
further includes:
means, coupled to the support member, for rotating the support
member about an axis perpendicular to the reaction surface.
34. The apparatus of claim 25, wherein the support member is
mounted within a shadow of the sample so that the radiant energy
does not directly strike the support member.
35. The apparatus of claim 25, wherein the support member includes
three sample contact pointed defining a support plane and
contacting the sample.
36. The apparatus of claim 25, wherein the support member consists
of a material essentially transparent to the radiant energy.
37. The apparatus of claim 25, wherein the means for generating
radiant energy includes a plurality of lamps; and the energy
distribution means comprises:
a lamp housing having a lamp seat for each of the plurality of
lamps, each lamp seat having a reflective surface with an
individually specified curvature, tilt and position with respect to
a plane parallel to the reaction surface.
38. The apparatus of claim 32, wherein the means for generating
radiant energy includes a plurality of line a lamps; and the energy
distribution means comprises:
a lamp housing having a plurality of lamp seats, one lamp seat for
each of the plurality of linear lamps, each lamp seat having a
reflective surface with an individually specified curvature, tilt
and position with respect to a lane parallel to the reaction
surface.
39. The apparatus of claim 38, wherein the reflective surfaces of
the lamp seats have conical curvatures.
40. The apparatus of claim 38, wherein the reflective surfaces of
the lamp seats have a first portion with a first tilt with respect
to the plane parallel to the reaction surface, and a second portion
with a second tilt with respect to the plane parallel to the
reaction surface, and wherein the average of the first tilt and the
second tilt equals the individually specified tilt for the
reflective surface.
41. The apparatus of claim 39, wherein the reflective surfaces of
the lamp seats have a first portion with a first tilt with respect
to the plane parallel to the reaction surface, and a second portion
with a second tilt with respect to the plane parallel to the
reaction surface, and wherein the average of the first tilt and the
second tilt equals the individually specified tilt for the
reflective surface.
42. The apparatus of claim 25, further including:
means, coupled to the reaction chamber, for sensing a temperature
of the reaction surface.
43. The apparatus of claim 25, further including:
means, coupled to the means for generating, for controlling
intensity of the radiant energy.
44. The apparatus of claim 37, further including:
means, coupled to each of the plurality of lamps, for individually
controlling intensity of each of the plurality of lamps.
45. An apparatus for growing an epitaxial layer on a sample having
a reaction surface, the sample absorbing heat causing energy; the
apparatus comprising:
a reaction chamber having a wall;
means, coupled wit the reaction chamber, for cooling the wall of
the reaction chamber;
support means, mounted within the reaction chamber, for supporting
the sample within the reaction chamber, and including a thermally
inert support member contacting the sample;
means mounted with the reaction chamber for generating heat causing
energy and directing the heat causing energy on the reaction
surface.
46. The apparatus of claim 45, wherein the heat causing energy is
radiant energy, and the sup-port member comprises a material
essentially transparent to the radiant energy.
47. The apparatus of claim 45, wherein the the support member is
mounted within a shadow of the sample so that the heat causing
energy does not directly strike the support member.
48. The apparatus of claim 45, wherein the support member includes
three sample contact points defining a support plane and contacting
the sample.
49. The apparatus of claim 46, wherein the reaction camber includes
a window on the reaction chamber through which the radiant energy
enters the reaction chamber, and wherein the window consists of a
material that absorbs a long infrared range of radiation generated
by the means for generating radiant energy, and has a thickness
sufficient to filter the long infrared range of radiation so that
the long infrared range does not heat inside the reaction
chamber.
50. The apparatus of claim 45, wherein the support means
includes:
means, coupled to the support member, for rotating the support
member about an axis perpendicular to the reaction surface.
51. The apparatus of claim 7, further including:
means, coupled to the plurality of linear lamps, for individually
controlling intensity of each of the plurality of linear lamps.
52. An apparatus of supplying a flow of a gas reactant over a
reaction surface on a sample, the sample absorbing radiant energy
within a given range of wavelengths, comprising:
a reaction chamber having a window essentially transparent to
radiant energy in the given range;
means, counted with the reaction chamber, for supporting the sample
within the reaction chamber, so that the reaction surface on the
sample faces the window;
means, in gas flow communication with the reaction chamber, for
supplying a flow of reactant gas to the chamber between the window
and the reaction surface;
pump means, having an exhaust port in gas flow communication with
the reaction chamber, for pumping gas out of the reaction chamber
to maintain a reduced pressure within the reaction chamber; and
a reactant distribution means, mounted in the reaction chamber
between the reaction surface and the means for supplying reactant
gas, and essentially transparent to radiant energy in the given
range, for directing a distributed flow of reactant gas essentially
perpendicular to the reaction surface;
wherein the fraction surface is between the reactant distribution
means and the exhaust port, and wherein the reactant distribution
means, reaction surface and exhaust port provide for an essentially
radially symmetric gas flow path over the reaction surface through
the reaction chamber.
53. The apparatus of claim 52, wherein the reactant distribution
means includes:
a plate, mounted between the window and the reaction surface
forming receiving compartment for the reactant gas, the plate
essentially transparent to the given range of radian energy and
having a plurality of perforations providing distributed gas flow
communication between the receiving compartment and the reaction
surface.
54. The apparats of claim 53, wherein the means for supplying a
flow of reactant gas includes:
a plurality of gas ports connected to supply reactant gas, in gas
flow communication with the receiving compartment.
55. An apparatus for inducing a controlled reaction on a reaction
surface on a sample, the sample absorbing radiant energy within a
given range of wavelengths, and characterized by a nonuniform
distribution of that loss, the apparatus comprising:
a reaction chamber having a wall and a window essentially
transparent to radiant energy in the given range;
means, coupled with the reaction chamber, for cooling the wall of
the reaction chamber;
support means, mounted with the reaction chamber, for supporting
the sample within the reaction chamber, so that the reaction
surface faces the window, the support means including a support
member within the reaction chamber supporting the sample, and
means, coupled of the support member, for rotating the support
member about an axis perpendicular to the reaction surface;
means, mounted with the reaction chamber outside the window, for
generating radiant energy in the given range;
energy distribution means, mounted with the means for generating,
for distribution the radiant energy in the given range to form a
controlled distribution having essentially rectangular symmetry of
radiant energy at the reaction surface of the sample, and wherein
the controlled distribution of radiant energy offsets the
nonuniform distribution of that loss while the sample is
rotated;
means, in gas flow communication with the reaction chamber, for
supplying a flow of reactant gas to the chamber between the window
and the sample; and
a reactant distribution means, mounted in the reaction chamber
between the reaction surface of the sample and the means for
supplying reactant gas, and transparent to radiant energy in the
given range, for directing the flow of reactant gas to create a
distributed flow essentially perpendicular of the reaction surface
on the sample.
Description
FIELD OF THE INVENTION
The present invention relates to apparatus for inducing a process
such as chemical vapor deposition on a reaction surface of a
sample, in which uniform heat distribution and distribution of
reactant are desirable. More particularly, the present invention
provides a reaction chamber for chemical vapor deposition, or other
processes, on semiconductor wafers in which gradients in
temperature across the sample and in concentration of reactant
across the reaction surface are minimized.
DESCRIPTION OF RELATED ART
Chemical vapor deposition processes are exemplified by the process
and apparatus described in U.S. Pat. No. 4,496,609 entitled
CHEMICAL VAPOR DEPOSITION COATING PROCESS EMPLOYING RADIANT HEAT
AND A SUSCEPTOR to McNielly et al. The CVD apparatus includes a
reaction chamber in which a sample is supported. The sample is
heated to a reaction temperature and a reactant gas is supplied to
the reaction chamber. When the reaction gas contacts the heated
reaction surface of the sample, a film of a desired material is
grown. One type of film is an epitaxial semiconductor layer grown
on top of another semiconductor wafer.
In CVD processes growing single crystal films, it is very important
to avoid temperature gradients across the reaction surface. The
temperature gradients cause crystallographio slip which degrades
the quality of the CVD grown film and causes non-uniform
growth.
In addition, in CVD processes, it is desirable that the thickness
of the grown film is uniform over the entire reaction surface.
Therefore, concentration and mass transport gradients of the
reactant gas which contacts the reaction surface should be
minimized.
The CVE apparatus shown in the McNielly et al. reference, uses what
is known as a cold wall reaction chamber. The reaction chamber has
cooled walls and a window through which radiant energy is
transmitted. Inside the reaction chamber, a susceptor which absorbs
the radiant energy, and supports the samples on which the CVD
process is to be performed, is mounted. Radiant energy heats the
susceptor, or both the susceptor and the samples directly.
A major component of heat loss out of the samples is radiant heat
loss. It is well known that the amount of heat lost due to
radiation is proportional to the fourth power of the temperature
gradient at a given point in the material. Therefore, at the edges
of the sample, much greater heat loss occurs than in the center of
the sample. The wide, heated susceptor minimizes the temperature
gradients at those edges and helps to maintain a uniform
temperature distribution across the reaction surface of the
samples.
Susceptors, however, are undesirable in that they are also subject
of the CVD process to varying extents. Therefore, they must be
cleaned or discarded periodically and replaced with new susceptors.
Also, as the CVD process operates, the surface of the susceptor on
which samples are supported becomes uneven. This causes voids
underneath the samples in which the C,D process may seep and cause
growth of a film on the backside of the sample. This is undesirable
in that it prevents the samples from laying flat, which may be
critical in subsequent processing steps along a semiconductor
manufacturing line.
In prior art CVD systems, it has been difficult to establish a
uniform flow of reactant gas onto the reaction surface.
Non-uniformity can result in nonuniform growth of the film. The
difficulty in establishing a uniform flow arises, in part, from
interference with the gas flow dynamic by the susceptor, and other
sample support mechanisms. Also, the gas flow dynamic is disturbed
by the requirement that the gas port be mounted out of the path of
the radiant energy illuminating the sample.
SUMMARY OF THE INVENTION
The present invention provides a reaction chamber using controlled
radiant heating of a sample without a susceptor to establish
uniform temperature distribution across the sample, and providing a
distributed flow of reactant across the reaction surface.
According to one aspect, the present invention provides an
apparatus for supplying radiant energy over a sample having a
reaction surface. The sample absorbs at least a component of the
radiant energy and is characterized by a non-uniform distribution
of heat loss, such as may be caused by radiant heat loss in a cold
wall reaction chamber. The apparatus comprises a reaction chamber
and a sample support member which supports the sample within the
reaction chamber. The support member does not behave as a
susceptor, and in one embodiment is formed of a material which is
essentially transparent to the radiant energy.
A source of radiant energy, such as an array of lamps or a single
lamp, is mounted with the reaction chamber so that direct radiant
energy is transmitted through a window in the reaction chamber to
the reaction surface of the sample. A lamp housing supports the
lamps between the window on the reaction chamber and a reflecting
surface on the housing. The reflecting surface includes a lamp seat
for each lamp in the array with an individually specified position,
curvature and tilt with respect to the reaction surface. Thus, the
direct radiant energy from the lamps and radiant energy reflected
from the reflecting surfaces on the lamp housing combines to form a
controlled distribution of radiant energy at the reaction surface
which offsets the nonuniform distribution of heat loss on the
sample and minimizes temperature gradients on the reaction
surface.
According to a second aspect, the invention provides an apparatus
supplying a flow of reactant over a reaction surface on a sample
being heated by radiant energy. The apparatus, according to this
aspect, includes a reaction chamber having a window transparent to
the radiant energy absorbed by the sample. A support member within
the reaction chamber supports the sample so that the reaction
surface faces the window. A source of reactant gas is coupled
through a gas port to the reaction chamber between the window and
the reaction surface. A reactant distribution plate, mounted
between the gas port for the source of reactant gas and the
reaction surface, causes distributed flow of reactant gas over the
reaction surface.
The reactant distribution plate, according to one embodiment, forms
a reactant gas receiving chamber between the window of the reaction
chamber and the distribution plate. The distribution plate includes
a plurality of perforations having a pattern which determines the
distribution of reactant gas flow. The source of reactant gas
supplies gas to the receiving chamber which behaves as a plenum for
distributing the flow of reactant gas directly onto the reaction
surface. An exhaust port is supplied in the reaction chamber for
letting gas out of the reaction chamber to maintain the distributed
flow of reactant. In one embodiment, the reactant distribution
plate, the reaction surface and the exhaust port are in line so
that the support mechanism does not disturb the flow of reactant
gas onto the reaction surface. This causes a symmetrical pressure
gradient over the reaction surface which maintains the distributed
flow of reactant with minimum concentration gradients over the
reaction surface.
According to a third aspect, the invention provides an apparatus
for inducing a controlled reaction on a reaction surface on a
sample, which combines in a single system, a lamp housing
establishing a controlled distribution of radiant energy over the
reaction surface with a reactant distribution system establishing
the uniform distribution of reactant flow.
Other aspects and advantages of the present invention can be
determined upon review of the figures, detailed description and the
claims which follow.
BRIEF DESCRIPTION O THE FIGURES
FIG. 1 is a cross-sectional view of a preferred embodiment of a
reaction chamber according to the present invention.
FIG. 2 is a view of the mechanism for translation and rotation of
the sample support member for the reaction chamber of FIG. 1.
FIG. 3 is an enlarged view of the lamp housing for use with the
reaction chamber of FIG. 1.
FIG. 4 is a view of the lamp housing showing the individually
specified position, curvature and tilt of each of the lamp seats
for the lamp housing.
FIG. 5 is a view of the lamp housing illustrating the air cooling
ports along the lamp seats.
FIG. 6 is an enlarged side view of the sample support member for
the chamber of FIG. 1.
FIG. 6A is a top view of the sample support member illustrating the
position of the support pins.
FIG. 7 is a diagram showing top and side views of the reactant gas
distribution baffle for the reaction chamber of FIG. 1.
FIG. 8 is a cross-section cut at line 8--8 through the reaction
chamber as shown in FIG. 1, illustrating the symmetrical reactant
gas port arrangement.
FIG. 9 is a block diagram of one embodiment of the lamp intensity
control system according to the present invention, using an analog
control loop.
FIG. 10 is a circuit diagram for the ratio controller of FIG.
9.
FIG. 11 is a block diagram of an alternate embodiment of the lamp
intensity control system, using a digital control loop.
DETAILED DESCRIPTION
A detailed description of a preferred embodiment of the present
invention is described with reference to the figures.
A. REACTION CHAMBER OVERVIEW
FIG. provides a side view of the reaction chamber 10 and lamp
housing 11 according to the present invention. Reaction chamber 10
includes three major areas. The first area, generally designated by
the reference numeral 12, forms a wafer transport and support
compartment for the reaction to be performed. The second area,
generally designated by the reference numeral 13, forms a reactant
gas receiving compartment. The third compartment, generally
designated by the reference numeral 14, forms a path for a flow of
exhaust gases from the chamber.
A sample support member 15 is mounted within the chamber on a
mechanism for rotation and translation of the support member 15.
The mechanism for translation and rotation is shown in FIG. 2.
The support member supports a sample 16, such as a slice of
semiconductor material, with a reaction surface 17 facing the lamp
housing 11. The structure of the support member 15 is illustrated
with reference to FIGS. 6 and 6A. The support member 15 is a "cold
support means" in the same sense that the reaction chamber is a
cold wall reaction chamber. That is, the support member 15 is
designed so that it does behave as a susceptor of the energy
inducing heat in the sample. Further, it remains cool relative to
the sample, so that the reaction is minimized on the support member
15.
The lamp housing 11 includes a head piece 18 and a base piece 19
The base 19 and head 18 are secured together to form a plenum for a
liquid cooling medium. The liquid enters input nozzle 20 and exits
output nozzle 21, after flowing through the path defined by the
fins 22, 23, 24, 25, 26, 27, 28 and 29, which are secured to the
head piece 18 and the channels 30, 31, 32, 33, 34, 35, 36 and 37,
which are cut in the base piece 19. The cooling medium may be water
in a preferred system, but any suitable liquid can be used.
The base piece 19 further includes an air cooling plenum through
which a cooling gas flow enters from nozzle 38 and/or 39. The
detailed structure of the base 18 of the lamp housing 11 is
described with reference to FIGS. 3-5.
The base 19 of the lamp housing 11 includes a plurality of lamp
seats formed by concave reflective surfaces which distribute
radiant energy according o a controlled pattern on the reaction
surface 17 of the sample 16 in the reaction chamber. The reaction
chamber 10 is a cold wall chamber which is formed basically of a
stainless steel or aluminum cylinder 40 with cooling fluid passages
(e.g. 41 and 42) a surrounding the interior of the chamber.
The chamber can be evacuated through the pump flange 43 to a
relatively high vacuum state. As the sample 16 is heated by the
radiant energy, the exterior of the reaction chamber 10 remains
cool. Significant heat loss from the sample 16 occurs therefore by
radiant heat loss. Heat loss also occurs due to convection in to
the carrier gas.
The chamber 10 is sealed between the lamp housing 11 and the
receiving compartment 13 by a quartz window 44 and O-ring 44A. The
quartz window 44 is transparent to the range of radiation which is
absorbed by the sample 16 to cause radiant heating of the sample.
The window 44 could be formed of any suitable material which is
essentially transparent to the preferred range of radiant energy
for a given application.
Quartz utilized for the window 44 absorbs a portion of the long
wavelength IR light of the output spectrum of the lamps. It is
desirable to prevent this long IR light from entering the reaction
chamber 10 and heating the walls and distribution plate. Thus, the
window is formed 1/2 to 3/4 inches thick, to act as an IR filter
and a sink for heat resulting from absorption of the long IR
radiation.
The receiving compartment 13 is coupled to receive a reactant gas
through channel 45 and a plurality of reactant ports 46, 47 and 48,
as illustrated in FIG. and a fourth port shown in FIG. 8. The
arrangement of the gas ports in the receiving compartment 13 is
more clearly shown with reference to FIG. 8.
Gas flows through the gas ports into the receiving chamber 13. A
baffle 49 with a plurality of perforations (shown in FIG. 7) forms
the boundary between the receiving compartment 13 and the main
reaction compartment 12. The baffle is formed of quartz material or
other material transparent to the range of radiation to be absorbed
by the sample 16.
The baffle 49, in combination with the receiving compartment,
operates to distribute the reactant gas over the reaction surface
17 of the sample 16 so that concentration and mass transport
gradients which may cause irregularities in the reaction process
are minimized across the reaction surface 17.
The main chamber 12 is further characterized by vacuum port 50
which is schematically illustrated. This port allows for insertion
and removal of sample 16 to and from the reaction chamber 10. Any
well known sample handling process and mechanism can be used.
Opposite the vacuum port 50 is flange 51. This flange 51 can be
used for a quick access port to the reaction chamber. Additionally,
a second vacuum port could be added on this flange 51.
In an operational system, the flange 51 is sealed shut, as is the
vacuum port 50, when the reaction is being carried out.
The third compartment 14 of the reaction chamber 10 is a narrowed
cylindrical extension of the main compartment 12. Thus, the
vertical wall 40 is coupled to horizontal wall 52 through which
cooling fluid flows in passage 53. Wall 52 is coupled to vertical
wall 54 which extends to a sealed rotation and translation
mechanism as shown in FIG. 2. An exhaust port 55 is formed in the
wall 54 inside the exhaust compartment, which is coupled to the
pump flange 43. The pump flange 43 is coupled to a vacuum pump
which draws gas out of the reaction chamber 10.
Thus, in operation, a sample 16 is placed on the support member 15
so that the reaction surface 17 sits on a reaction plane facing the
source of radiant energy in the lamp housing 11. The chamber is
evacuated and the lamps are energized. The lamps generate a
controlled distribution of radiant energy at the reaction plane in
the compartment 12 of the reaction chamber 10. The controlled
distribution offsets the distribution of radiant heat loss on the
sample 16 and causes an essentially uniform temperature across the
entire reaction surface 17.
The temperature of the sample 16 is detected through the tubular
interior 56 of the support member 15, as shown in FIG. 2. Other
alternative positions for the sensor would eliminate need for a
tubular interior 56 of the support member 15. For instance, the
temperature sensor could be placed above the sample to directly
detect reaction surface temperatures, if desired.
Reactant gas can be supplied to the receiving chamber 13 before,
during or after desired temperature is reached. Receiving chamber
13 behaves as a plenum for the reaction gas which passes through
the baffle 49 in a controlled distribution onto the reaction
surface 17. A pump connected to the pump flange 43 draws exhaust
gases through the exhaust port 55. Because this exhaust port 55 is
located in the exhaust compartment 14, a gas flow path is
established by which gas from the baffle 49 flows down over the
reaction surface 17 of the sample 16 and essentially symmetrical
around the sample into the exhaust chamber 14. This establishes a
basically symmetrical gas flow dynamic which minimizes
concentration gradients across reaction surface 17.
The gas flow is schematically illustrated by the arrows labeled
"REACTANT" and "EXHAUST" in FIG. 1.
B. ROTATION AND TRANSLATION MECHANISM
FIG. 2 illustrates the mechanism for rotating and translating the
support member 15 of FIG. 1. The support member 15 is coupled to a
mount flange 60. The mount flange 60 is coupled to a rotation shaft
61 which extends into a rotary feedthrough 62, such as are
commercially available from Ferrofluidic, Inc. Feedthrough 62
behaves as a bearing and a vacuum seal.
The shaft 61, after passing through the feedthrough 62, is coupled
to pulley 63, which is driven by a motor to cause rotation of
support member 15. Rotation of the support member 15 is required
because, in the preferred embodiment, the lamps seats in the lamp
housing are formed to establish a rectangular symmetry for the
distribution of radiant energy at the reaction plane. By rotating
the support member, a sample with a circular symmetry receives a
circularly symmetrical distribution of radiant energy
absorption.
The rate of rotation can be varied from less than one to over 1000
revolutions per minute depending on the application.
The shaft 61 is sealed by a window 64 and mounted on a bearing 65.
The window 64 can be mad.RTM.of calcium fluoride (CaF) or quartz or
any material suitable for the emission spectrum of the sample. A
radiant energy detector 66 is mounted at the base of the bearing 65
and detects, through the cylindrical bore of the shaft 61 and the
support member 15, the temperature of the sample 16 in the reaction
chamber. Detector 66 is mounted on a support base 67.
Translation of the support member 15 is accomplished by one or more
worm gears, e.g., worm gear 68 is shown. One worm gear is used in a
preferred embodiment. This structure is mounted with the wall 54 of
the reaction chamber 10. Wall 54 is coupled to a translation plate
69 on which bearing 70 is mounted to receive the worm gear 68. The
translation plate is coupled to vacuum bellows 71 which allows for
expansion of the wall of the reaction chamber. The vacuum bellows
71 is mounted to a support plate 72 on which the feedthrough 62 is
mounted. The support plate 72 also includes bearing 73 for worm
gear 68. The worm gear is coupled to a belt drive system
exemplified by the pulley 74 in the figure. This belt drive system
is used to raise and lower the support member 15 in the reaction
chamber.
Raising and lowering the support member 15 is used during insertion
and removal of the sample 16, for changing the relationship of the
reaction surface 17 to the distribution of radiant energy caused by
the lamp housing 11, and for affecting gas flow dynamics in the
compartment 12. Thus, the sample 16 may be moved closer to or
farther away from the lamps and baffle as desired for a particular
reaction. In the preferred system, the sample position is designed
to be 0.5 to 2 inches from the bottom of baffle 49, with the
optimal position usually at 1 inch.
C. LAMP HOUSING
FIG. 3 is an enlarged view of the lamp housing base 19 with
schematic representation of the lamp intensity control 300 and
temperature detector logic 301. The lamp intensity control system
is described with reference to FIGS. 9-11. The lamp housing base 19
supports a plurality of linear heat lamps, such as tungsten halogen
lamps, in the form of elongated tubes which extend through the lamp
housing. The lamps are designated L1 through L7 in FIG. 3. The
lamps L1-L7 are of selected lengths to accommodate the circular
housing shape. The peak energy per unit length of all lamps is the
same.
Each of the plurality of lamps L1 through L7 is mounted within a
respective lamp seat 101, 102, 103, 104, 105, 106 and 107. Each
lamp seat is a concave reflective surface adapted to direct
reflected radiant energy from the lamp to the reaction surface of
the sample. The concave lamp seats are preferably formed with the
curved or conical geometries, but could take on straight line
geometries (triangle, pentagon, etc.) if required for a given
application or method of manufacture. The reflective surfaces are
highly polished and coated with gold or another high reflectivity
coating in the preferred system, for reflectivity and
durability.
The combination of reflected radiant energy with the direct radiant
energy from the lamp forms a controlled distribution of radiant
energy at the reaction surface to offset any irregularities in the
heat loss distribution on the sample, so that temperature gradients
across the reaction surface are reduced.
In the preferred system, the curvatures of the lamp seats are
elliptical and a corresponding lamp is mounted essentially at the
near focal point of the ellipse. Therefore, the lamp seat can be
characterized as having a position, tilt and curvature individually
specified to provide the controlled distribution of radiant energy
at the reaction surface. In the embodiment illustrated in FIG. 3,
the position and tilt of the focal point of each lamp seat is set
out in the following table; where the X position is a reference to
the center line of the lamp housing and reaction chamber; and the Y
position is the height above the base of the lamp housing.
TABLE 1 ______________________________________ LAMP NO. TILT X
POSITION Y POSITION ______________________________________ L1
24.degree.00' -4.125 0.813 L2 11.degree.30' -2.840 1.313 L3
7.degree.30' -1.450 1.563 L4 0.degree.00' 0.00 1.313 L5
-7.degree.30' 1.450 1.563 L6 -11.degree.30' 2.840 1.313 L7
-24.degree.00' 4.125 0.813
______________________________________
The curvature of each of the lamp seats is illustrated in FIG.
4.
FIG. 3 also shows a clear view of the gas cooling plenum through
which gas is supplied at ports 38 and 39. The cooling plenum
includes a plurality of interconnected channels 110-118 through
which air is supplied. The air in these channels is coupled into
the lamp seats through ports, such as port 119 at lamp L1. The
lamps are mounted in the openings illustrated in FIG. 3 spaced away
from the reflective surfaces in the lamp seats so that passage for
cooling air is allowed. The cooling air flows out of the ports,
such as port 119, and flows over the lamps and out to the
atmosphere.
As mentioned above, FIG. 4 illustrates the curvatures of the lamp
seats 101-107. Each lamp seat is comprised of a split elliptical
channel which extends along the respective lamp tube. Each half of
the split elliptical channel is cut to form an elliptical curve
defined by the classical definition of an ellipse:
E=sin.theta.
The elliptical curvature used in the preferred embodiment:
Each ellipse in the split ellipse is offset by a tilt of 10.degree.
from the tilt of the lamp seat which is set forth in Table 1 above.
Thus, each curvature can be characterized by two focal points, such
as focal points A and B for lamp seats 101 and 107, focal points C
and D for lamp seats 102 and 106, focal points E and F for lamps
seats 103 and 105, and focal points G and H for lamp seat 104.
Thus, each half of a lamp seat can be characterized by the position
of its focal point, and the angle of the long axis of the ellipse
defined by the focal point to the vertical as set out in the
following table:
TABLE 2 ______________________________________ ANGLE FOCAL POINT TO
VERTICAL X Y ______________________________________ A (+)(-)
14.degree.00' (+)(-) 4.129 0.769 B (+)(-) 34.degree.00' (+)(-)
3.881 0.879 C (+)(-) 1.degree.30' (+)(-) 2.948 1.297 D (+)(-)
21.degree.30' (+)(-) 2.682 1.351 E (-)(+) 2.degree.30' (+)(-) 1.574
1.557 F (+)(-) 17.degree.30' (+)(-) 1.305 1.592 G (-) 10.degree.00'
(+) 0.135 1.325 H (+) 10.degree.00' (-) 0.135 1.325
______________________________________
It can be seen that the average angle of focal points A and B
equals to the tilt of lamp seat 101, and so one for each lamp
seat.
By using a split ellipse lamp seat, less energy is reflected off of
the elliptical surface back into the lamp and more is directed to
the reaction surface.
FIG. 4 also illustrates that the central focus of each lamp seat is
directed to create a controlled distribution of the energy along a
reaction plane 120. The reaction plane would be located in the
reaction chamber at the position of the reaction surface on the
sample 16.
This controlled distribution for the embodiment shown is determined
by computer simulation of the radiation profile generated by the
lamps in the lamp housing for a preferred operating condition to
establish a known profile, taking into account reflection and
refraction at the window and baffle. Each lamp-lamp seat
combination generates an energy profile determined by the position
of the lamp and the position of the images created by the
elliptical surfaces defining the lamp seat. The intensity of each
image is in turn determined by the capture angle of the
corresponding elliptical reflector. The combined effect of all
seven lamp-lamp seat sources creates a controlled distribution of
radiant energy at the reaction surface of the sample.
The distribution of radiant energy is then varied by individually
controlling, in the lamp intensity control system of FIGS. 9-11,
the intensity of the lamps L1-L7 to achieve a distribution required
for a given reaction. Individual lamps can be controlled to
establish, in combination with selected lamp seat design, any
desired pattern of intensity.
The distribution can also be varied by moving the sample up and
down in the reaction chamber.
FIG. 5 illustrates the plurality of air cooling ports and the
elongated nature of the lamp seats in the lamp housing base 19.
Each lamp seat 101 through 107 is an elongated channel of a highly
reflective surface. Along the center of each channel is a plurality
of gas ports 140 allowing flow of a cooling gas over the lamps
mounted in the housing. The lamp ports 140 are coupled to the
plenum which receives gas through ports 38 and 39 as discussed with
reference to FIGS. 1 and 3.
In alternative systems, the ports 140 could be replaced by slots.
Also, ports or slots could be placed outside the lamp seat to
provide a cooling medium for removing heat from the quartz window
on the reaction chamber.
Alternative energy distribution mechanisms, such as absorbing
filters, coatings, or other optics could be used to establish a
controlled distribution of radiant energy in the reaction
chamber.
D. SUPPORT MEMBER
FIGS. 6 and 6A illustrate the structure of the support member 15.
The support member is supported by the shaft 150. On top of the
tubular shaft 150 sits a plate 151. Coupled to the plate 151 are
three support pins 152, 153 and 154. Guide posts 155, 156 and 157
are used to prevent shift of the sample 16 off of the support pins
152, 153 and 154, when the support member 15 is being rotated, and
when inserting the sample 16 onto the support member 15.
The support pins are located as illustrated in FIG. 6A. Thus, pins
152, 153 and 154 are located 120.degree. apart from each other
around the circumference of the support plate 151 and define a
support plane. The guide posts 155, 156 and 157 are secured to the
perimeter of the support plate 151.
The support pins 152, 153, and 154 are formed so that the points
(e.g.. 160 on pin 152) are very sharp, having a radius of less than
one millimeter. Thus, the contacts on the sample 16 are small,
allowing for very little heat loss through the support pins. Thus,
the amount of area of the contacts on the support member 15 is much
less than the surface area of the reaction surface 17 of the sample
16.
E. REACTANT DISTRIBUTION SYSTEM
FIG. 7 illustrates the baffle 49 which is used for causing a
distributed flow of reactant gas over the reaction surface 17 of
sample 16 in the reaction chamber shown in FIG. 1. The baffle 49,
illustrated in FIG. 7, is for a sample which is formed of a 6 inch
diameter semiconductor wafer. Thus, a plurality of perforations
formed in the baffle 49 fall within a 6 inch diameter outer hole
limit. The perforations are typically 2 mm in diameter, 4 mm center
to center, and formed in parallel rows within the 6 inch diameter
circular field illustrated in FIG. 7. Thus, there are approximately
900 holes in the field.
Around the outer perimeter 200 of the baffle 49, a structural
tubular member 201 is formed. The side view of the baffle 49
illustrated in FIG. 7 shows the structure of the support tube 201.
It is basically a 4 mm thick tubular extension so that the baffle
49 sits on top of a length of tube with a 233 mm outer diameter and
a 219 mm inner diameter. The baffle 49 itself is 2 mm thick and
8.983 inches in diameter. The length of the tubular support
structure is 0.629 inches. The material of which the baffle is
formed is optically polished quartz produced by Heraeus Amersil,
T08 commercial type E. It can be formed of any material which is
essentially transparent to the range of radiant energy to be
distributed over the reaction surface 17 of the sample.
FIG. 8 is a cross-sectional view along line 8-8 of FIG. in the
reaction chamber 10 through the gas supply ports 46, 47, 48, 170
and the plenum 45, showing how the reactant gas is distributed
symmetrically into the receiving chamber 13. The reactant gas is
supplied through valve 200 through tube 201 into plenum 45. The
plenum splits into four individual channels to the ports 46, 47, 48
and port 170. The channel 202 from port 47 to the valve 200 is
shown and the channel 203 from port 48 to the valve 200 is
shown.
A view of the manner in which the channel 202 bypasses the port 46
is shown at 205. It can be seen that a separate channel 206
proceeds below the channel 202 from the valve 200 to port 46. The
channel 206 and the channel 202 are separated by wall 207. The bore
208 proceeds from the channel 206 into the receiving chamber 13
through the port 46. The channel to port 170 is formed in a similar
manner as the channel 206 to port 46.
An alternative system for providing individual flow channels, could
be implemented using tubes plumbed outside the body of the reaction
chamber. This alternative may eliminate problems with debris from
machining the channels shown in FIG. 8.
By providing individual flow channels in the plenum for reactant
gas to the distributed ports, a more uniform reactant flow into the
receiving compartment 13 is accomplished. The embodiment described
is designed to supply from a few hundred cubic centimeters per
minute to over 50 liters per minute.
F. LAMP INTENSITY CONTROL SYSTEM
The lamp intensity control system by which the intensity of each of
the lamps is individually controlled is described with reference to
FIGS. 9-11. FIG. 9 illustrates an analog control loop for the
lamps. FIG. 10 is a circuit diagram of the ratio control circuitry
for the system of FIG. 9. FIG. 11 is a block diagram of an
intensity control system with a digital control loop.
The system illustrated in FIG. 9 is based on an analog control loop
which controls the intensity of each of the lamps in the lamp
housing 900. The lamps in the lamp housing 900 are schematically
represented by lines labelled LC, L1, L2, or L3. Lamp LC is in the
center of the lamp housing 900. The two lamps labelled L1 are
adjacent lamp LC. The two lamps labelled L2 are adjacent lamps L1.
Finally, the two lamps labelled L3 are the outside lamps on the
lamp housing 900.
Each of the lamps is coupled to a silicon controlled rectifier SCR.
Thus, lamp LC is coupled to SCR 901. The two lamps labelled L1 are
coupled to SCR 02. The two lamps labelled L2 are coupled to SCR
903. The two lamps labelled L3 are coupled to SCR 904. A ratio
control power supply 905 delivers four power outputs. Power output
906 is coupled to SCR 90. Power output 907 is coupled to SCR 902.
Power output 908 is coupled to SCR 903. Power output 909 is coupled
to SCR 904. The maximum power output on each of the four power
outputs is set to 100% of the lamp driving intensity. However, in
the ratio control power supply, manual potentiometers SC 910 for
lamp LC, Sl 911 for lamps L1, S2 912 for lamps L2, and S3 913 for
lamps L3 are provided so that the ratio of power output for each of
the lamps is individually controllable.
Note that in the system described, the lamp pairs L1, L2 and L3 are
controlled by a single power output. This provides symmetrical
operation of the lamp housing 900. For embodiments in which a
symmetrical operation is not desired, individual power outputs are
supplied by a straight forward extension of this design.
The ratio control power supply 905 is illustrated in FIG. 10 in
more detail.
As input to the ratio control power supply 905, a command power is
supplied on line 914 from a temperature controller 915. The
temperature controller 915 is formed by a PID analog control
circuit. A set point temperature is supplied to the temperature
controller across line 916 from system computer 917. A voltage
proportional to the temperature is supplied across line 950 from an
optical pyrometer 918. The optical pyrometer 918 corresponds to the
sensor 66 of FIG. 2.
Infrared emissions 919 from the sample wafer 920 are detected by
the pyrometer 918 to generate the output voltage V.sub.T
proportional to the temperature on line 950. Radiant energy 921 is
delivered to the sample wafer 920 from the lamp housing 900, to
complete the control loop.
In operation, the potentiometers 910-913 are set to control
distribution of radiant energy on the wafer 920, in combination
with the design of the reflective lamp seats in the lamp housing
900 as discussed above.
Manual setting of the ratio control power supply 905 through the
potentiometers 910-913 provides rather rough control. The ratio
control power supply 905 could be easily adapted to include
digitally controllable potentiometers, which, in turn, can be
controlled by the system computer 917. By this manner, extremely
precise control of the relative powers of the lamps is
achieved.
The ratio control power supply 905 is illustrated in FIG. 10. The
command power 914 is connected to jumper 1000. Jumper 1000 has a
first output 1001 which is connected to the positive input of
operational amplifier 1002. A second output of jumper 1000 is
connected on line 1003 to a ground terminal 1004. A resistor 1005
is connected from the ground terminal 1004 to the line 1001. The
operational amplifier 1002 is connected in a unit gain
configuration and acts as a buffer for supplying the command power
signal on line 1006 as input to four individual power amplifiers
AMP3 1007 for lamps L3, AMP2 1008 for lamps L2, AMPl 1009 for lamps
L1, and AMPC 1010 for lamp LC. Each of the four amplifiers is
identical so the schematic of AMPC 1010 is the only one
described.
Coupled to each lamp, as described with reference to FIG. 9, is a
manually settable potentiometer. Thus, potentiometer 913 is coupled
to AMP3 1007, potentiometer 912 is coupled to AMP2 1008, and
potentiometer 911 is coupled to AMP1 1009. The potentiometer 910 is
included within the schematic of AMPC 1010.
The amplifier schematic for AMPC is described. The signal on line
1006 is supplied through resistor 1011 to the negative input of
op-amp 1012. The output of op-amp 1012 is coupled on line 1013
through feedback resistor. This provides a unity gain power
amplifying stage. The output on line 1013 is coupled through input
resistor 1015 to the negative input of op-amp 1016. The output of
op-amp 1016 is supplied through resistor 1017 to output line 1018.
Output line 1018 is coupled to feedback circuit 1019. The feedback
circuit 1019 includes a capacitor 1020 coupled from line 1018 to
the negative input of op-amp 1016. Also, the feedback circuit
includes a two-position switch 1021. In the first position, the
switch is coupled to terminal 1023. Terminal 1023 is coupled
through resistor 1022 to line 1018. The second position of the
switch is coupled to terminal 1024 which is connected directly to
line 1018. The common terminal of the switch 1021 is coupled to
potentiometer 910 which is set to control the ratio of the output
power. The switch 1021 sets the range of output power by
controlling the amplification of the amplifier stage. In the first
position of switch 1021, the gain of the amplifier stage is from
one to two, depending on the setting of the potentiometer 910. In
the second position, the gain of the stage is from zero to one,
again depending on the setting of the potentiometer 910.
The positive input to op-amp 1016 is coupled to a zero setting
cirouit 1025. The zero setting circuit includes a first terminal
1026 coupled to a 15 volts power supply The terminal 1026 is
connected through resistor 1027 to potentiometer 1028. Likewise,
potentiometer 1028 is coupled through resistor 1029 to a -15 volt
supply terminal 1030. The potentiometer 1028 is adjusted to set the
zero level of the amplifier stage.
The amplifier stage includes a common terminal 1031 which is
coupled to line 1032 as an output of the amplifier stage. A zener
diode 1033 is coupled between lines 1032 and 1018 to provide over
voltage protection.
Lines 1018 and 1032 are coupled to output jumper 1034. Likewise,
the outputs from AMPs 1-3 are coupled to output jumper 1034. The
output jumper 1034 is coupled to the SCRs illustrated in FIG.
9.
As an alternative to the analog control loop of FIG. 9, a digital
control loop can be utilized as illustrated in FIG. 11 to provide
more precise control of the intensities of the lamps. In FIG. 11,
the elements which are identical to corresponding elements in FIG.
9 are given the same reference numerals. In the system of FIG. 11,
the voltage V.sub.T on line 950 representing the temperature of the
wafer on line 917 for the digital control loop is supplied directly
to the system computer 1100. The system computer 1100 implements a
closed loop software PID controller to generate a power command
value. The power command value is then multiplied by the software
set ratios to generate four individual lamp power signals on line
1101. Lines 1101 are coupled to ratio controller 1102 which
consists of four individual amplifier stages. The four stages of
ratio controller 1102 are similar to those described in FIG. 10,
except that the potentiometers in the amplifier feedback loops are
eliminated. To control the ratio of output power in the ratio
control power supply 1102, the input to each of the four amplifier
stages is individually controlled by the system computer 1100.
Using the digital control loop of FIG. 11, the intensity of the
various lamps for a preferred power distribution can be set with
precision. In addition, for a given application, the computer can
be used to iteratively calculate and implement optimal lamp
intensities.
G. CONCLUSION
It can be seen that the present invention provides a superior
reaction chamber adapted particularly for chemical vapor deposition
on semiconductor wafers. The chamber is characterized by a
controlled distribution of radiant energy over the sample in the
chamber, and controlled distribution of reactant gas into the
chamber over the sample reaction surface.
A first mechanism by which reactant gases are distributed onto the
sample consists of a window made of a material which is transparent
to the wavelength of the radiant source and a reactive gas
distribution plate made of the same material situated near the
window. The radiant source is positioned to the atmosphere side of
the window and reactant gases are introduced into the reaction
chamber between the distribution plate and the window. The
processing sample is placed next to the distribution plate facing
the radiant source. The reactive gases are introduced directly onto
the sample through openings in the gas distribution plate. The gas
distribution plate is further used to control gas dynamics of the
reactant gases.
This gas distribution mechanism allows the radiant source to be
mounted on the same side of the sample as the direction of flow of
the reactive gas onto the sample to optimize sample reaction.
Further, it allows a wide range of freedom for the sample support
so that it does not interfere with the radiant source or lie in the
path of the reactant gas flow. This mechanism for controlling a
distribution of reactive gases is useful in any reaction chamber
where interference from the sample support mechanism in the
introduction of gas and introduction of gas from the same side as
the energy source are desired.
The second mechanism forming part of the reaction chamber according
o the present invention consists of a housing for an array of
linear lamp sources and reflectors that provides for control of the
distribution of illumination over a sample. Each lamp seat consists
of a reflector with one or two elliptically shaped surfaces.
Through refinements in the position, eccentricity and tilt of the
elliptical surface, the distribution of the direct and reflected
radiant energy is controlled. This design allows accurate control
of the radiant energy overall a sample surface where a certain
energy profile is desirable.
The controllability of the distribution o radiant energy over a
sample surface allows the achievement of uniform temperature across
the sample. This is true even when the ample will have a
non-uniform distribution of heat loss. Thus the desired radiant
energy distribution can compensate for radiant heat loss of a
sample at various temperatures in a reaction chamber.
In the foregoing description, a single example of a gas
distribution plate and a single example of the lamp housing are
described. It will be recognized by those skilled in the art that
for a given geometry of sample and type of reaction desired, the
distribution of energy and of reactive gas can be adapted by
adapting the lamp housing reflector surfaces and the gas
distribution baffle. In addition, the rotatable support member may
be replaced by a stationary support if the symmetry of heat loss
from the sample are matched with the symmetry of the distribution
of radiant energy supplied at the reaction surface.
The foregoing description of preferred embodiments of the present
invention has been provided for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise forms disclosed. Obviously, many
modifications and variations will be apparent to practitioners
skilled in this art. The embodiments were chosen and described in
order to best explain the principles of the invention and its
practical application, thereby enabling others skilled in the art
to understand the invention for various embodiments and with
various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be
defined by the following claims and their equivalents.
* * * * *